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Flashcards in B&B 1 PNS Deck (94):

What are the CNs?

I Olfactory → Smell
II Optic → Vision
III Oculomotor → Eye Movement
IV Trochlear → Eye Movement (SO4)
V Trigeminal → Face: Sensory, Motor
VI Abducens → Eye Movement
VII Facial → Facial Power
VIII Vestibulocochlear → Hearing & Balance
IX Glossopharyngeal → Throat Sensation
X Vagus → Parasympathetic, Palate Power
XI Accessory → Neck Turning
XII Hypoglossal → Tongue Power


What are the locations where a lesion could occur?

1. Brain
2. Cranial Nerves
3. Brain Stem
4. Spinal Cord
5. Nerve Roots
6. Peripheral Nerve
7. Muscle


What does the Neuro exam consist of?

►Mental Status (Orientation, Attention, Memory, Language, Spatial Orientation)
►Cranial Nerves
►Motor Strength, Tone
►Reflexes, Coordination, Gait


Nerve Roots to Know
Peripheral Roots to Know

Nerve Roots
• C5, C6, C7
• L4, L5, S1

Peripheral Roots
• Medial, Ulnar, Radial
• Sciatic, Femoral, Perineal


What is Capacitance?

How to deal with it?

The cell membrane is a capacitor because it accumulates charge on either side

The larger the axon diameter, the higher the capacitance. More SA = more accumulation of charge

The goal is to decrease accumulation of charges by putting an insulator around the cell membrane.

Myelin decreases capacitance.
• Oligodendrocytes (CNS)
• Schwann Cells (PNS)
The AP is recharged at each Node of Ranvier


Active Current
Passive Current

►Active Current
ion movement through ion channels

►Passive Current
is the shuttling of charge along a neuronal process

Saltatory Conduction:
Active Current → Passive Current → Active Current → Passive Current ... etc

(the charge is more "tunneling" rather than "jumping")



"gwee-ANNE bear-EH"

►Myasthenia Gravis




– autoimmune CNS
– Abs attack Oligodendrocytes → degrade myelin

– autoimmune PNS
– Abs attack Schwann cells → degrade myelin
– segemental demyelination
– PNS can re-myelinate

►Myasthenia Gravis
– autoimmune
– Abs destroy Ach receptor on NMJ

– death of UMN & LMN
– paralysis of voluntary muscles and loss of ability to swallow, speak, and breathe

– infection
– virus kills cell bodies of ventral horn
– death of α-motor neuron → paralysis

– Prevents pre-synaptic Ach release → flaccid paralysis



(C = cephalon)

►Forebrain (ProsenC)
– Cerebrum
– Basal Ganglion
– Thalamus
– Hypothalamus

►Midbrain (MesenC)

►Hindbrain (RhombenC)
– Pons
– Cerebellum
– Medulla


What are the various nerve fibres?

How does diameter and conduction velocity relate?

greatest Diameter
greatest velocity
smallest Diameter
smallest velocity


Of the various nerve fibres, which are myelinated?

A & B fibres are myelinated

C fibres are unmyelinated


Slow Adapting Receptors


Rapidly Adapting Receptors

►Merkel Receptors
– slow adapting
– found in superficial skin layers
– provide touch info

►Pacinian Corpuscle
– rapidly adapting
– found in deep subcutaneous tissue ("onion")
– response to deep pressure and high frequency vibration
– reports on change

(remember Meissner's Corpuscles are for light touch)


UMN Lesion


• Paralysis or paresis (weakness) of the involved muscles

• Increased muscle tone (hypertonia)

• Spasticity

• Hyperactive deep reflexes

• no or little muscle atrophy (atrophy of disuse)

• diminished or absent superficial abdominal reflexes, and abnormal reflexes (e.g. Babinski’s response) → toes go up


LMN Lesions


• weakness

• flaccid paralysis of the involved muscles

• decreased muscle tone, muscle atrophy with fasiculations

• can have fibrillations

• degeneration of muscle fibers over time and histologic - reaction degeneration

• diminished or absent reflexes (areflexia)

• Babinski → toes go down



What is it?

A neurological phenomenon in which stimulation of one sensory pathway leads to automatic, involuntary experiences in a second sensory pathway.



What is a common form?

→ color synesthesia:
individual letters of the alphabet and numbers (collectively referred to as graphemes), are "shaded" or "tinged" with a color.

• abherernt connections can be made after neuronal cell death (eg. man with stroke)

CAUSE ... "cross- activation"?


Special Senses
General Senses

Which CNs are involved?

Olfaction - Cr. I
Vision - Cr. II
Taste - Cr. VII and IX
Hearing and balance - Cr. VIII

Cr. V (trigeminal)
All spinal nerves (except cervical 1)


How do we sense deep sensation?

(stretch-sensitive ion channels)

Pacinian Corpuscle
– Has 20 to 60 concentric lamellae composed of fibrous connective tissue separated by gelatinous material
– In the center of the corpuscle is the inner bulb, a fluid-filled cavity with a single afferent unmyelinated nerve ending.
– Adapt rapidly


How do we sense taste?

Chemicals (salty, sweet, sour, etc) binds to receptor →
triggers cascade → opens Na+ channels


What do we call the somatosensory map?



Two-Point Discrimination
– helps assess nerve damage

What properties of the mechano-sensory system allows us to discriminate two points pushing on our skin?

(1) Receptor Density
(2) Size of the receptive fields


What is the smallest size that can be detected between 2 points ....

on the back?

on the fingertips?

30-40 mm

1-2 mm


Lateral Inhibition

What is it?

Lateral inhibition
– blocks the lateral spread of excitatory signals and therefore increases the degree of contrast in the sensory pattern perceived in the cortex
(creates "trough" in middle)


What are the 4 elementary attributes of a stimulus:

– Modality
– Intensity
– Duration
– Location


What are the two different kinds of somatic motor neurons?

– skeletomotor
– innervate extrafusal fibres

– fusimotor
– innervate intrafusal fibers
– 2 types:
(1) Static → Bag2 & chain fibers
(2) Dynamic → Bag1 fibers


Muscle Spindles

What are they?

– Stretch-sensitive mechanoreceptors
– found in virtually all skeletal muscles
– particularly dense in muscles concerned with fine, manipulative tasks
– intrinsic hand muscles
– highest density in neck muscles


What are the two different types of intrafusal fibres in muscle spindles?

– smaller
– larger
– no striations in middle region and swells to enclose nuclei

– half as long as bag, smaller diameter
– has a row of nuclei at middle • “chain”


Anatomical summary of the muscle spindle...

3 “kinds” of intrafusal fibers
- Bag1, Bag2, & chain

2 “kinds” of motor innervation
- static γ mn
- dynamic γ mn

2 “kinds” of sensory innervation
- Group Ia and II afferents


Muscle Spindles


►Muscle Spindles: we get muscle length and velocity info
– Group Ia give us velocity and length information
– Group II only provide length information

►Variable motor innervation allows for flexible sensitivity...
– γ dynamics increases velocity sensitivity
– γ statics increases length sensitivity


What is the Hoffmann Reflex?

– Activating a stretch reflex without stretching the muscle
– Uses electoral stimulus
– "Stretch reflex without stretch"


What does a Tendon Tap stimulate?

– activates muscle spindle

– not the golgi tendon
(we never really talked about this)


Name the structures from Superficial to Deep on the head

►Epidural Space
Periosteal Layer of DM
Meningeal Layer of DM
►Subdural Space
Arachnoid Mater
►Arachnoid Space (CSF)
Pia Mater
Cerebral Cortex


Corpus Callosum

What is the function?

"callosal commissure"

Fx: connects the 2 hemispheres


What is on the anterior side of ...




– Optic Nerve
– Mamillary Bodies

– Bulge of the basal (anterior) pons

– Pyramids
– Olive (on either side)


What is on the posterior side of ...




– Superior Colliculi
– Inferior Colliculi

Cerebellar Pedcules (CP)
– Superior CP
– Middle CP
– Inferior CP

– Fasciculus Gracilis (medial)
– Fasciculus Cuneatus (lateral)
– Obex: point at which the 4th ventricle narrows to become the central canal of the spinal cord.


What is in front and behind of the Central Sulcus?

Precentral gyrus
- anterior to central sulcus
- primary motor area

Postcentral gyrus
- posterior to central sulcus
- primary somatosensory area


What is the name of the fissure on the medial surface in occipital lobe?

Calcarine Fissure


What are the three types of fibre tracts in the CNS?

►Commissural Fibres
– connect hemispheres
(eg) corpus callosum

►Association Fibres
– connect areas within a hemisphere

►Projection Fibres
– project to / from cortex



Which structures?


– processes sensory info (except olfactory)
– processes motor info
– integrates higher order cognitive / emotional info, regulation of cortical activity
– "gatekeeper" to the cortex

– functionally part of limbic system
– coordinate / integrate endocrine, autonomic, homeostatic function

– part of basal ganglia
– modulate / integrate voluntary movement & muscle tone


BASAL GANGLIA are large masses of gray matter (nuclei) deep within the cerebral hemispheres

What structures?

– Caudate Nucleus (putamen)
– Lenticular Nucleus (globus pallidus)
– Subthalmic Nucleus

– Substantia nigra


Limbic Lobe

What structures?

● parahippocampal gryri
● cingulate gryri
● subcallosa gryri
● dentate gryri
● hippocampus


CSF Circulation

Choroid Arteries & Plexus
(Ependymal Cells)
Lateral Ventricle
⬇︎ Inter-ventricular Foramen
Third Ventricle
⬇︎ Cerebral Aquaduct
Fourth Ventricle
⬇︎ Subarachnoid Space
→ Lateral Foramina of Luschka
→ Medial Foramen of Magendie
⬇︎ Central Canal
Spinal Cord

● Arachnoid Granulations
● Superior Sagital Venous Sinus


What is congenital Hydrocephalus?

What causes it?

– Congenital condition
– Excess CSF in brain

►Communicating / Non-obstructive
– due to def absorbing CSF into sinus
– (eg) due to damage of arachnoid granulations from purulent bacterial meningitis

►Non-communicating / Obstructive
– outflow from ventricles is obstructed, preventing subarachnoid circulation and reabsorption


A patient is in the hospital with bacterial meningitis. There is a risk for this patient developing hydrocephalus.

How would this hydrocephalus develop?

Damage to arachnoid granulations



– spontaneous contraction of a single muscle fiber that occurs when the muscle fiber has lost its nerve supply and is normally not visible through the skin

– spontaneous firing of an entire motor unit, causing contraction of a group of muscle fibers and may be visible through the skin.


When a nerve is damaged, what happens to the distal & proximal sections?

►Distal Section
– axon will degenerate
– connective elements of the so called distal stump often survive

►Proximal Section
– Axonal sprouting occurs → grow toward the nerve ending → results from growth promoting factors
secreted by Schwann cells that attract axons toward the distal stump


How successful is peripheral nerve regeneration?

● Often reversible!

● Regeneration allows for considerable, although not full, recovery (e.g. fine motor control may be permanently impaired because some motor neurons are guided to an inappropriate motor fiber)

NOTE: recovery of peripheral nerves from damage far surpasses that of central nerve pathways


What are the major types of neuropathies?

● Diabetes related
● Alcohol related
● HIV related
● Drug related
● Genetic


Diabetic Neuropathies

Describe ...

►Axonal in nature
– Length dependent and slowly progressive
– Sensory > Motor
– Loss of ankle jerk reflexes
– Nerve conduction study shows low amplitude and mild slowing of conduction speed


Guillain Barre Syndrome

"gwee-ANNE bear-EH

– Rapid onset involving arms and legs
– Motor and sensory are equally affected
– Areflexia
– Slow conduction velocity, conduction block and temporal dispersion evident on nerve conduction study


What test could we use to investigate ...?
– lower motor neuron (LMN) disease or primary muscle disease
– defects in transmission at the NMJ

– study of electrical activity arising from muscles at rest and those that are actively contracting


What is an MUP?

How can we use it?

Muscle Unit Potential
– has a characteristic size and duration in any given muscle
– the number of MUPs will decrease if LMNs, roots, or nerves are injured so that motor axons are severed and muscle fibers are denervated
– During reinnervation & nerve repair, MUPs increase in amplitude and duration and in some cases become polyphasic → provides evidence of reinnervation


Single fiber EMG

– Allows for recording of action potentials from single muscle fibers using very fine electrodes

– Permits measurement of muscle fiber density within a given motor unit

– may be especially useful for the diagnosis of disorders involving motor neurons (e.g. ALS) and the NMJ


In the CNS ...

What is the most common excitatory neurotransmitter?

What is the most common inhibitory neurotransmitter?

Excitatory: glutamate

Inhibitory: GABA




– gait impairment
– unclear (“scanning”) speech
– visual blurring
– hand incoordination
– tremor with movement


Sensory ataxia


What does it result from?

Clinical Findings?

S/S – Ataxia with numbness

Results from disorders that affect proprioceptive pathways in peripheral sensory nerves, sensory roots, posterior columns of the spinal cord or medial lemnisci

produced by polyneuropathies that prominently affect large, myelinated sensory fibers and by myelopathies, including those resulting from
– Friedreich ataxia
– neurosyphilis
– vit B12 deficiency


Sensory ataxia

Clinical Findings?

– defective joint position
– vibration sense in the legs (sometimes arms)
– unstable stance with Romberg sign (inability to maintain stance with eyes closed)
– gait of slapping or slippage quality



– Generalized process affecting peripheral nerves
– weakness is relatively symmetrical from the beginning
and progress bilaterally
– reflexes are lost in affected parts but particularly at the ankles
– sensory complaints and loss of sensation are most pronounced distally (feet first, then hands)



– disease of spinal roots with asymmetrical neurologic signs with an erratic distribution (e.g. proximal in one limb and distal in another)

– Weakness and zones of sensory loss correspond to involvement of one or more spinal or cranial roots

– Pain in the sensory distribution of the roots is a common feature.



– most often root compression by disease of spinal column with pain, sensory, motor and reflex change solely in the distribution of one nerve root

– Limitation of sensory loss to one of the dermatomes.



– weakness and sensory loss in territory of a single peripheral nerve


Mononeuritis multiplex

Mononeuritis multiplex
– cumulation of multiple mononeuropathies can be difficult to differentinate from polyneuropathy



– only one limb affected but the motor, sensory and reflex loss does not conform to pattern of several adjacent nerve roots of nerves


Myelin Sheath
Axonal involvement

How to differentiate pathology?

– Myelin sheath involvement will have temporal dispersion and delay in nerve conduction or conduction block in nerve conduction studies

– Axonal involvement will have decrease in CMAP amplitude


What kind of problems will we see?
Anterior horn pathology
Nerve Root Compression
Peripheral Nerve Involvement

►Anterior horn involvement → will show only motor problems

►Nerve root compression and plexus involvement → will have dermatomal distribution

►Peripheral nerve involvement → will have both motor and sensory problem with stock and glove distribution

►Neuromuscular junction and muscle problem → will have pure motor findings


Nerve Conduction Studies

How are they performed?

Surface electrodes are placed on the skin for stimulation of accessible peripheral nerves, and the resulting compound action potential is recorded over the nerve or over a muscle innervated by the nerve being studied


Nerve Conduction Studies

When do we see slowed conduction?

• Guillain Barre syndrome
• chronic inflammatory demylinating polyneuropathy
• Charcot Marie Tooth disease

►Sites of focal compression



• involves submaximal stimulate applied to mixed nerves at an intensity too low to produce a direct motor response

• Stimuli evoke a muscle contraction (H-wave) with a relatively long latency due to action of Ia spindle afferent fibers which travel via dorsal root of the spinal gray matter where they synapse with lower motor neurons

• Absence of H-reflex suggests pathologic conditions along this pathway and is often a result of radiculopathies or polyneuropathies involving spinal roots or proximal parts of peripheral nerves (e.g. Guillain Barre syndrome)


F wave

F wave
• is a long latency response, following the direct muscle potential, that is evoked by supramaximal stimulation of motor- sensory nerves

• Produced by antidromic (retrograde) stimulation of motor axons, which results in invasion of APs into their cell bodies in the spinal cord and evokes a second (reflected) APl that travels along motor axon to muscle

• Absence of F-wave implies pathologic conditions of spinal roots or proximal parts of peripheral nerves



What happens during weeks 1 & 2?

►Formation of bi-laminar embryonic disc

Early Blastula



What happens during week 3?

• Gastrulation establishes three germ layers and axial orientation of embryo

• Epiblast first migrate downwards through primitive streak to displace hypoblast forming the endoderm

• Epiblast then will migrate into the space created during delamination to become mesoderm

• The epiblast cells left over after gastrulation becomes the ectoderm

NOTE: EtOH can interfere with gastrulation resulting in fetal alcohol spectrum disorder



After Gastrulation, what happens during weeks 3-4?

• Process initiated by induction signals from notochord underlying ectoderm
• Process involves formation of neural plate and neural folds and closure of folds to form neural tube
• Anterior neuropore closes at ~23 days and the posterior neuropore about 2 days later
• Failure to close neuropores can result in anencephaly or spina bifida depending on which pore is affected
• Neural crest cells (NCCs) are incredibly pluripotent they migrate to future head and neck regions (pharyngeal arches) to contribute in formation of face, nasal cavities, mouth, larynx, pharynx, neck
• First arch syndrome = abnormalities in first arch NCC migration → congenital abnormalities of eyes, ears, mandible, palate



Vesicle Formation

Brain develops from portion of neural tube cranial to 4th

3 primary brain vesicles:
• Forebrain (prosencephalon)
• Midbrain (mesencephalon)
• Hindbrain (rhombencephalon)



What does the spinal cord develop from?

• develops from portion of neural tube caudal to 4th pair of somites
• The development of sensory and motor areas is initiated by opposing concentration signal molecules which induces distinctive patterns of subsequent development within the neural tube
→ Ectoderm adjacent to neural plate produced BMPs (bone morphogenetic proteins)
→ Notochord influences overlying cells at ventral midline of neural groove to express sonic hedgehog (SHH)


After neural tube fusion ...

• what do dorsal cells produce?

• what do ventral cells produce?

dorsal cells produce BMPs

ventral cells produce SHH

►This establishes an opposing gradient


What are the three basic zones of the spinal cord?

►Alar plate
dorsal horn: sensory

►Basal plate
ventral horn: motor

►Marginal Zone
presumptive white matter


Guillain Barre syndrome


• ~2/3 of GBS cases occur weeks after an infection such as C. jejuni, CMV, EBV, Mycoplasma pneumonia or influenza virus
• Some cases has been associated with immunizations
• Molecular mimicry is the main pathophysiological mechanism


Guillain Barre syndrome


• Most patients have acute neuropathy reaching a peak in under 4 weeks, weakness, hyporeflexia or areflexia, and raised protein concentrations in CSF

• Neurophysiological studies play important role in diagnosis → motor nerve stimulation, F waves and bilateral tibial H-reflexes


Guillain Barre syndrome

What is the Ddx?

• In patients without sensory involvement, disorders like poliomyelitis, myasthenia gravis, electrolyte disturbance
(hypokalemia), botulism or acute myopathy need to be considered

• Once the diagnosis of an acute peripheral neuropathy is established, GBS is the most common (alternatives to consider = diphtheria, vasculitis, porphyria, tick paralysis, and toxic neuropathy)


Guillain Barre syndrome

Clinical Course

• First symptoms are pain, numbness, paraesthesia, or weakness in the limbs
• The weakness may initially be proximal, distal or a combination of both
• Numbness and paraesthesia usually affect the extremities and spread proximally
• Facial nerves are often affected
• In 25% of cases, weakness of respiratory muscles require artificial ventilation
• Autonomic involvement is common and causes urine retention, ileus, sinus tachycardia, HTN, cardiac arrhythmia, and postural hypotension
• Disease reaches its nadir by 2 weeks in most cases and in 4 weeks in nearly all


Guillain Barre syndrome

What is the outlook for the patient?

• Between 4-15% of patients dies and up to 20% are disabled after a year despite modern treatment

• Even in those who recover well, residual weakness and loss of motor units can usually be detected on clinical and electrophysiological exam and could explain the fatigue that is a common problem

NOTE: Our PBL pt had a full recovery (but developed carpal tunnel syndrome later due to his job which was unrelated to his previous GBS)


Guillain Barre syndrome


• Plasma exchange and IV Ig are effective immuno-therapies for adult and paediatric patients if given during first few weeks of disease

• Immunoabsorption therapy is an alternative to plasma exchange (does not require using human blood product) by removing Ig from circulation without need for replacement with albumin or fresh frozen plasma due to the lower loss of albumin

• Supportive care → monitor and manage respiratory failure and airway compromises; monitoring and management of autonomic nervous system dysfunction (tachycardia, HTN, bladder dysfunction and bowel dysmotility)

• Prophylaxis for DVT due to immobilization → heparin

• Pain management if present → gabapentin and carbamazepine


Guillain Barre syndrome


• Outlook is worse in elderly patient
• In children, recovery is more rapid and more likely to be complete and death is are
• In adults and children, severity of disease at nadir, expressed as being bedbound or requiring artificial ventilation, has usually been identified as an adverse prognostic factor
• Patients with a rapid onset phase are more likely to do badly
• Most patients with AMAN (acute motor axonal neuropathy) variation make a good recovery
• In several studies, patients with previous C. jejuni infection have had more severe disease and a delayed recovery
• Presence of CMV has been shown to predict delayed recovery and EBV infection has been associated with milder forms


Guillain Barre syndrome

Prognosis ... (more) ...

• Most patients with AMAN (acute motor axonal neuropathy) variation make a good recovery
• In several studies, patients with previous C. jejuni infection have had more severe disease and a delayed recovery
• Presence of CMV has been shown to predict delayed recovery and EBV infection has been associated with milder forms


Exam of hand reveals impaired cutaneous sensation in the thumb, index finger, middle finger, and adjacent half of the ring finger with thenar muscle weakness

What is affected?

Splits ring finger!

Only peripheral nerves does this (NOT nerve root).
Therefore, this is a peripheral nerve that is affected:
Median Nerve


What are the 3 groups of peripheral nerves?

• large and myelinated
• smaller and myelinated (ex proprioception)
• small and unmyelinated (ex. temp)
• small and unmyelinated


Bulbar palsy

What is it?

impairment of function of CN 9, 10, 11, 12 which occurs due to a LMN lesion either at nuclear or fascicular level in the medulla oblongata or from lesions of the lower CNs outside the brainstem


►Patient #1:
CSF shows ↑ WBCs

►Patient #2:
CSF shows ↑ protein

What does each patient have?

Patient 1 has infection

Patient 2 likely has GBS



The axon of the a motor neuron...
(a) is unmyelinated
(b) generates the CMAP waveform
(c) traverses the dorsal root ganglion

(b) generates the CMAP waveform

"compound muscle action potential"




In PNS ...
• protective sheath surrounds each nerve fibre

• surrounds fascicles (bundles of nerve fibres)
• continuous with the arachnoid membrane.

• surrounds bundles of fascicles


Infections of the scalp can spread into the meninges by the:

emissary veins


A typical example of a pseudo-unipolar neuron is

neuron in the dorsal root ganglion


How do the lateral and 3rd ventricles communicate?

How do the 3rd and 4th ventricles communicate?

►Lateral and third ventricles
→ communicate via the interventricular foramen

►3rd and 4th ventricles
→ communicate via the cerebral aqueduct.


The neural plate is induced by:



Sympathetic postganglionic neurons are derived from ...

Neural Crest